Recent years have seen various efforts to encourage energy saving and resource saving for protecting our planet.
In terms of the energy saving, Japanese Patent Laid-Open No. S57-96852 discloses a technique of producing a highly insulation box unit. In the disclosure, vacuum insulation material disposed between the inner box and the outer box of an insulation box unit is integrally foamed with rigid urethane foam.
From the resource-saving point of view, recycling disposal appliances, such as a refrigerator and a television, has become increasingly valued; in particular, as for refrigerators, various ecological efforts have been made.
In an insulation box unit that is the major component of the refrigerator, metallic materials including iron plates are recyclable without great difficulty. Whereas, plastics, especially rigid urethane foam made of thermosetting resin, which is employed in quantity for the insulation material of the refrigerator, cannot be melted for recycling. Therefore, such materials have been conventionally buried, burnout, or used as a filler. To address the conventional disposal of plastics, a new processing-technology makes a proposition to decompose polymeric material, with supercritical, or sub-critical water employed in the process.
For example, Japanese Patent Laid-Open Application No. H10-310663 introduces a method of recovering polyurethane resin through decomposing. In the disclosure, polyurethane resin is subjected to chemical decomposition employing supercritical, or sub-critical water to recover raw material compound and reusable raw material derivatives in the polyurethane resin.
Japanese Patent No. 2885673 introduces a method in which polymeric material is chemically treated with supercritical or sub-critical water so as to be decomposed into oil components.
As the need for energy saving grows, there has emerged a need for providing a refrigerator having higher insulation efficiency; a larger area occupied by vacuum insulation material, i.e., an extended coverage of the vacuum insulation material to the surface area of the outer box has been required.
However, too-high coverage by the insulation material may cause troubles. Although conventional coverage within the range from 30% to 40% has no problem, a coverage exceeding the range may seriously affect the structural strength of the insulation box unit. In the box unit, the outer box and the inner box are integrally bonded with rigid urethane foam disposed between the two boxes, whereby structural rigidity of the insulation box unit is remained. However, employing a different kind of material, i.e., the vacuum insulation material in larger area in an insulation wall layer automatically decreases the thickness of the rigid urethane foam. Thus, the lack of rigidity caused by the thinned polyurethane foam can result in deformation in the insulation box unit.
Particularly, the deformation of the box unit becomes more pronounced in a refrigerator having two or more doors; the doors are not allowed to tightly fit to the body due to the distortion, which makes undesired gap at the gasket, thereby inviting poor insulation efficiency.
To avoid the distortion, there is a well known method in which density of the rigid urethane foam is greatly increased so as to provide large bending modulus that is an index of rigidity. The rigid urethane foam having an extensively increased density, however, increases conductive heat transfer in solids. As a result, against the purpose of heat insulation, the insulation efficiency of the rigid urethane foam will be largely affected. This contributes to decreasing insulation efficiency of the insulation box unit that is the essential target.
As the coverage of the vacuum insulation material increases, endothermic amount of the insulation box unit decreases; accordingly, this encourages energy saving. However, the efficacy of the energy saving moves down along saturation curve, after all, it is not rational in terms of acquiring a rewarded outcome that offsets investment costs.
Besides, when the coverage of vacuum insulation material is increased higher than it should be, it becomes necessary to prepare the material with nonstandard size and shape, and also necessary to dispose the material in a difficult-to-task section in the manufacturing processes. The facts have caused problem of extensive increase in the cost of the vacuum insulation material and production costs.
In the multi-layered insulation section formed of the rigid urethane foam and the vacuum insulation material, if a rigid urethane foam-filled wall has not enough thickness, the expanding foam decreases its flow performance. As a result, an inconsistent filling or poor filling decreases the insulation efficiency of a polyurethane foam-layer. Therefore, the insulation efficiency of a multi-layered insulation section may be smaller than it was expected, or on the contrary, the insulation efficiency may get worse. In particular, the structure having an extremely increased coverage of the vacuum insulation material has a risk of decreasing the insulation efficiency, because that the hard-to-flow polyurethane layer covers almost the inner face of the insulation box unit.
Furthermore, a poor insulation efficiency of vacuum insulation material itself further decreases the insulation capability in addition to the aforementioned decrease in the polyurethane part of the multi-layered insulation section. Accordingly, it has not achieved a noticeable energy-saving effect in spite of getting the coverage of the vacuum insulation material as high as possible.
From the viewpoint of resource-saving and recycling, employing the aforementioned method disclosed in Japanese Patent Laid-Open Application No. H10-310663 can recover raw material compound of the polyurethane resin and reusable raw material derivatives from rigid urethane foam.
The method, however, is not applicable for recycling an insulation box of a disposal refrigerator as its entirety; the supercritical water employing process cannot chemically decompose rigid urethane foam covered by the iron plate of the outer box or ABS resin of the inner box. On the other hand, various kinds of polymeric material, such as polypropylene resin for interior components, can be chemically decomposed by supercritical or sub-critical water. If an insulation box involving different kinds of members is subject to chemical decomposition, materials containing monomeric substances obtained from the process are dissolved into raw material compounds as impurity. Therefore, such raw material compounds having impurity is not reusable as rigid urethane foam.
In order to recover raw material compound of the polyurethane resin and reusable raw material derivatives as reusable industrial resource, it has been the essential issue that “pure” rigid urethane foam with no different members should be separated and classified from an insulation box unit to be discarded. Furthermore, it has been waited for an improved disposal method in which iron can be recovered so as to achieve high recovery efficiency as a whole system.
As another problem to be considered, the aforementioned raw material compound of the polyurethane resin and reusable raw material derivatives, which are obtained from the chemical decomposition, are determined by the chemical structure of the rigid urethane foam to be decomposed. That is, the chemical structure of the compound and derivatives depend on basic raw material forming the rigid urethane foam. It becomes therefore important that a recycling method suitable for the basic raw material forming rigid urethane foam should be employed.
Furthermore, it has been another challenge for encouraging recycling system that reusing the raw material compound of the polyurethane resin and reusable raw material derivatives obtained through chemical decomposition as insulation material for a refrigerator.
Besides, there has been a critical obstacle to promote recycling with high efficiency—proper methods of processing rigid urethane foam cannot be specified without identifying the basic raw material of the rigid urethane foam used for the insulation box unit as the major component of a disposal refrigerator.